Waste from aircraft lavatories is generally collected in a holding tank during flight, and removed after landing using airport facilities. A drain port is therefore provided on the aircraft fuselage for emptying the contents of the holding tank. When the tank is to be emptied, a device is placed over the port and the valve is opened for emptying the waste. The waste may be allowed to flow out of the tank under the force of gravity alone, or suction may be used to draw the waste from the tank.
A number of valve designs exist for such drain ports. One design which is particularly suitable for use with the present invention is disclosed in U.S. Pat. No. 4,098,427 ("the '427 patent") to Duckworth, which is incorporated herein by reference. A double sealing, two-door valve is shown there, with an inner door and an outer door enclosing the inner door.
Another typical design used for these applications employs a plug for sealing the port, in combination with a single door for providing a second seal outside the plug.
A particular concern of aircraft drain valves in general is to provide an adequate seal to prevent leakage. Because of the extremely cold temperatures at high altitudes, any liquid which leaks through a seal quickly freezes. The frozen material which thus forms can break off in flight, and constitutes a hazard to the aircraft. Another problem with the frozen material is that it jams the drain port valves shut so that they do not properly open when the waste holding tank is to be emptied after landing.
A similar problem affecting some drain port valves involves a build-up of residue in the area of the valve seal, which may occur if the valves are not attentively maintained. This residue can cause the valve door to stick in the closed position, making opening of the door more difficult.
It is therefore an object of this invention to provide a means for ensuring that drain port valves open regardless of whether leakage and freezing of waste material has occurred.
It is a further object of this invention to provide such a means which may be easily adapted to existing designs of drain port valves.